1. Field of the Invention
The present invention relates to a charged particle beam device, and a measuring method using the same.
2. Description of the Related Art
Currently, in the manufacturing line of semiconductors, technologies of measuring the dimension of a circuit pattern formed on a wafer in the middle of a process have a significant role for improvement of the yield. Conventionally, most of the measuring technologies have been based on optical microscopes. However, currently, measuring devices based on SEMs (hereinafter, SEM-based length measuring devices) have been widely spread due to micronization of semiconductor patterns.
Then, in recent years, diversification and three dimensional structures of materials used in the semiconductor devices have been advanced. Therefore, demands for dimension measurement among different types of materials and for dimension measurement of three dimensional devices are increasing.
As a means to obtain a contrast among different types of materials in an SEM, there is a method of performing energy discrimination of the secondary electrons detected in the SEM. Here, the “secondary electrons” include “true secondary electrons” (electrons of 50 eV or less, which are generated such that a primary electron beam is inelastically scattered inside a sample and excites atoms inside the sample, and electrons generated therefrom are released from the surface) and reflected electrons (having almost the same energy as the primary electrons, which are generated such that the primary electrons are backscattered inside the sample, and electrons get out of the surface). By making use of this, various measurements become possible by discriminating the secondary electrons sensitive for surface forms and the reflected electrons having information of embedded form under the surface. Hereinafter, secondary electrons include both of “true secondary electron” and the “reflected electron” unless otherwise specified.
Meanwhile, most of the three dimensional devices have shapes with high aspect deep grooves and deep holes. When measuring the dimension of the deep grooves and deep holes with the SEM-based length measuring device, efficient detection of secondary electrons having got out of the groove bottoms and hole bottoms is required. This is due to an effect of side walls. Many of the secondary electrons that can get out of the groove bottoms or hole bottoms are emitted in the vicinity of the optical axis of the primary electrons where the electrons are less subject to the effect of the side walls. Therefore, it is necessary to detect the secondary electrons emitted in the vicinity of the optical axis for observation and measurement of deep grooves and deep holes.
As an example of a configuration that enables the energy discrimination of the secondary electrons, there is a configuration disclosed in WO 01/075929 A. In WO 01/075929 A, a negative voltage is applied to a metal grid, and only the secondary electrons having passed through the metal grid are detected. In this case, to pass through the electrode grid, the secondary electrons need to have energy larger than the voltage applied to the grid, and thus the energy discrimination of the secondary electrons becomes possible.
Hereinafter, the metal grid to which the negative voltage used from the energy discrimination of the secondary electrons is applied is called “energy filter”. Meanwhile, as a configuration that enables the energy discrimination of the secondary electrons emitted in the vicinity of the optical axis, there is a configuration disclosed in JP-2001-357808-A. In JP-2001-357808-A, only secondary electrons are deflected outside the optical axis by an ExB deflector that is an optical element in which a magnetic field and an electric field are mutually orthogonal, and an energy filter is disposed between the ExB deflector and a detector.